The present invention relates to a modified xanthan gum which can directly be dissolved in an aqueous salt solution to thus impart a desired viscosity to the salt solution and a method for modifying xanthan gum.
Xanthan gum is a naturally-occurring high molecular weight polysaccharide produced by microorganisms such as Xanthomonas campestris, the aqueous solution thereof is stable over a wide pH range and likewise stable to salts and enzymes. Xanthan gum can be dissolved in aqueous solutions of salts and quite effectively serves to increase the viscosity of the aqueous salt solutions. For this reason, xanthan gum has widely been used in various field such as food industries and chemical industries. It has intensively been desired to uniformly dissolve xanthan gum in common salt aqueous solutions in particular in the food industries.
If xanthan gum is once dissolved in an aqueous solution of a salt, it shows a stable thickening effect. It is very difficult to completely dissolve xanthan gum in a solvent at a temperature of not more than room temperature if the solvent is an aqueous salt solution, in particular that having a high salt-concentration. There have been known several methods for dissolving xanthan gum in aqueous salt solutions.
For instance, one example thereof comprises two-stage operations. More specifically, this method comprises dissolving xanthan gum in water free of salts and then adding a desired salt to the xanthan gum solution. In addition, there has also been known a method comprising partially (about half) dissolving xanthan gum in an aqueous salt solution and then heating the partially dissolved xanthan gum solution.
In addition to the foregoing methods, there have been proposed a variety of methods for making the dissolution of xanthan gum in water easy. Examples thereof are a method in which xanthan gum is treated with a surface active agent (Japanese Patent Provisional Publication No. 63-230703); a method comprising admixing a water-retention material with xanthan gum (Japanese Patent Application Publication No. 60-4214); a method comprising covering xanthan gum with hydrolyzed gelatin (Japanese Patent Application Publication No. 1-159048); a method comprising incorporating a wetting agent and a dispersant into the aqueous salt solution (Japanese Patent Provisional Publication No. 63-54490); a method comprising incorporating silica into the aqueous salt solution (Japanese Patent Provisional Publication No. 57-3834); a method comprising treating xanthan gum with glyoxal (Japanese Patent Application Publication No. 61-61800); and a method comprising incorporating a cold water-soluble gum into xanthan gum treated with glyoxal (Japanese Patent Provisional Publication No. 56-92956).
If the foregoing two-stage method comprising the step of preliminarily dissolving xanthan gum in water free of salt is adopted for increasing the viscosity of an aqueous salt solution, complicated procedures are inevitably required. Moreover, xanthan gum cannot be uniformly dissolved in an aqueous salt solution even if a solution containing partially dissolved xanthan gum is heated over a long time period with stirring. In other words, part of xanthan gum still remains in the resulting solution as undissolved particles.
The foregoing methods which comprise the addition of third components such as surface active agents, water-retention materials, gelatin, wetting agents, dispersants and silica only show an effect of preventing the formation of undissolved lumps in water, but never provide xanthan gum which can directly be dissolved in an aqueous salt solution to thus thicken the salt solution.
As has been discussed above in detail, the conventional xanthan gum suffers from a problem that it is very hardly soluble in aqueous salt solutions.